This invention relates to voice compression and more specifically, to improving radio functions using voice compression.
With the advance of voice coding techniques, a radio frequency (RF channel) can be more efficiently utilized. Voice coding algorithms allow speech information to be compressed for less RF time spent in transmission or reception of a voice signal. Moreover, subsequent decoding will expand the compressed voice signal to reproduce the original voice, which occupies 100% of the audio time. It is this percentage difference between the RF channel air time and the actual voice audio time that improves the efficiency of the RF channel.
One such usage is time-division multiplexing (TDM) where two or more channels of information are transmitted over the same link. However, there are numerous other applications that can utilize this percentage difference between the RF channel air time and the actual voice audio time to more efficiently implement different functions, features or radio operations in a single radio.
In scanning, it often is desirable to assign a priority to one or more of the channels (or frequencies) to be monitored and to receive the signal on the highest priority channel whenever a signal is being received on the priority channel. In a typical priority channel scanning system, the priority channel or channels are continually sampled, monitored, or scanned for signals during the reception of signals on any of the many non-priority or lower priority channels. Whenever a priority signal is detected, only the priority signal is received until the priority signal terminates.
The sample time or period is of sufficient length to detect the presence of a signal on the priority channel, but is short enough to prevent the production of a substantial audible hole in the signal being received on the non-priority channel. The priority sample periods are generally taken at fixed intervals. The sample periods do not cause a substantial audible signal hole in the non-priority signal, however, the signal is muted during the sample period which can cause both annoyance to the listener and some loss of signal intelligibility. Thus, when scanning for RF channel activity while receiving an RF channel of interest, received audio information is lost while the radio is checking other RF frequencies or priority channels. The signal being received must be interrupted during the time that the synthesizer is on another frequency so that the radio can determine whether or not there is channel activity on that new channel. To scan a radio system composed of several RF priority channels the original channel has to be interrupted many times a second with a corresponding loss in audio quality. Hence, if scan is active during a received transmission, information is lost and this information results in the degradation of audio quality.
As previously described, when a radio is unmuted, receiving a non-priority mode channel during scan, the user or subscriber is blind to other non-priority activity due to the limited hole size that can be punched. Only the priority channels are scanned while receiving. This means that even if important information exists for a particular radio on another non-priority channel, the radio cannot receive it. The user is therefore completely unaware that other information exists. Accordingly, it is desirable to provide an improved priority channel monitoring method and system which provides a minimal signal loss on the non-priority channels.
Conventionally, data and control or signalling information, is sent either before or after the user's voice transmissions. Otherwise, "holes" would have to be punched in the audio to receive the data transmission and control or signalling signals in the middle of the voice signal. Therefore, there is a need to send embedding signalling during a voice signal without losing audio quality during a voice signal and without muting the speaker during the data transmission or reception.
Reciprocally, there are numerous transmission applications that can utilize the percentage difference between the RF channel air time and the actual voice audio time to send signalling or control signals or mere data to control a radio or provide it with data. Conventionally, data is sent at the start or at the end of a voice transmission. Typically, data is sent only to the receiver of the entire transmission. In other words, a subscriber or user cannot direct data only to one subscriber and voice to another subscriber. Moreover, data transmission during a voice transmission is usually delayed until after the user has finished transmitting his or her voice signal. Hence, it is desirable to be able to direct data by sending signalling or control information to define the receiver of the voice signal, separately from the receiver of the data signal. Additionally, it is desirable to receive data, status, or timing information, etc. during the voice reception without losing audio quality.